The present invention relates to a voltage-controlled predistorter that can be used in a predistorting linearizer. The function of the predistorter is to predistort an input signal in view of cancelling a distortion subsequently produced by an amplifier.
Microwave power amplifiers (solid state or travelling wave amplifiers) used in ground station transmitters and communication satellites should ideally be highly efficient and provide linear amplification over a wide range of input power. Obviously, the performance of these microwave power amplifiers is limited by the non-linearities of their inner parts or constituents. A wide variety of correction methods for a microwave power amplifier""s non-linearities have been proposed and implemented including power back-off, negative feedback, feed forward, etc. However, in most cases the efficiency of the linearized amplifier drops significantly with respect to the efficiency of the non-linearized amplifier specially when the amplifier input is a high crest factor modulated signal such as a CDMA (Code Division Multiple Access), NPR (Noise Power Ratio), or other types of signals.
Predistortion is one of the best cost-effective approaches to reduce the level of non-linear distortion generated by microwave power amplifiers while retaining relatively good power efficiency. Predistortion consists of introducing in the input microwave signal amplitude and phase distortion opposite to the distortion produced by the microwave power amplifier. In this manner, distortion is cancelled to obtain at the output of the power amplifier a signal that is an amplified replica of the input signal with almost no power efficiency decrease. Therefore, the function of a predistorter is to generate both inverse amplitude and phase non-linearity. Since the characteristics of a microwave power amplifier significantly change with temperature, the predistorter has to maintain the overall performance of linearity of the system and to follow the amplifier changes.
An object of the present invention is therefore to provide a predistorter for use in conjunction with an amplifier for predistorting an input signal in view of cancelling signal distortion subsequently produced by the amplifier.
More specifically, In accordance with the present invention, there is provided a predistorter for predistorting a RF signal subsequently injected in an amplifier, comprising:
a hybrid coupler comprising a RF input constituting an input of the predistorter supplied with the RF signal, a RF output constituting an output of the predistorter for supplying a predistorted version of the RF signal, a direct port, and a coupled port;
a first semiconductor component connected between the direct port and the ground;
a second semiconductor component connected between the coupled port and the ground; and
a controllable biasing-voltage supply connected to the first and second semiconductor components, thereby supplying the first and second semiconductor components with a controllable biasing voltage.
In operation, the predistorter produces a controllable predistortion of the RF signal related to the controllable biasing voltage to cancel a distortion subsequently produced by the amplifier.
In accordance with the present invention, there is also provided a predistorting linearizer channel amplifier for processing a RF signal subsequently injected in an amplifier, comprising:
a controllable input variable-attenuator and drive-amplifier circuit supplied with the RF signal to attenuate and amplify the RF signal;
the above described predistorter supplied with the attenuated and amplified RF signal to produce a predistorted RF signal;
a controllable output variable-attenuator and drive-amplifier circuit supplied with the predistorted RF signal to attenuate and amplify the predistorted RF signal before supply of the predistorted RF signal to the amplifier; and
a controller connected to the controllable input variable-attenuator and drive-amplifier circuit, the biasing-voltage supply, and the controllable output variable-attenuator and drive-amplifier circuit, this controller embodying a phase-shifting and amplitude-adjusting control function applied to the controllable input variable-attenuator and drive-amplifier circuit, the controllable biasing-voltage supply, and the controllable output variable-attenuator and drive-amplifier circuit in order to produce a predistortion of the RF signal which cancels a distortion subsequently produced by the amplifier.
In accordance with the present invention, there is also provided a predistorter for predistorting a RF signal subsequently injected in an amplifier, comprising:
a hybrid coupler comprising a RF input constituting an input of the predistorter supplied with the RF signal, a RF output constituting an output of the predistorter for supplying a predistorted version of the RF signal, a direct port, and a coupled port;
a first diode having an anode connected to the direct port and a cathode connected to the ground;
a second diode having an anode connected to the coupled port and a cathode connected to the ground; and
a controllable biasing-voltage supply connected to the direct port and to the coupled port, thereby supplying the direct and coupled ports with a controllable biasing voltage.
In operation, the predistorter produces a controllable predistortion of the RF signal related to the controllable biasing voltage to cancel a distortion subsequently produced by the amplifier.
In accordance with the present invention, there is further provided a predistorter for predistorting a RF signal subsequently injected in an amplifier, comprising:
a hybrid coupler comprising a RF input constituting an input of the predistorter supplied with the RF signal, a RF output constituting an output of the predistorter for supplying a predistorted version of the RF signal, a direct port, and a coupled port;
first and second diodes connected between the direct port and the ground, the first and second diodes being connected in head to tail configuration;
third and fourth diodes connected between the direct port and the ground, the third and fourth diodes being connected in head to tail configuration; and
a controllable biasing-voltage supply connected to the direct port and to the coupled port, thereby supplying the direct and coupled ports with a controllable biasing voltage.
In operation, the predistorter produces a controllable predistortion of the RF signal related to the controllable biasing voltage to cancel a distortion subsequently produced by the amplifier.
The present invention still further relates to a predistorter for predistorting a RF signal subsequently injected in an amplifier, comprising:
a hybrid coupler comprising a RF input constituting an input of the predistorter supplied with the RF signal, a RF output constituting an output of the predistorter for supplying a predistorted version of the RF signal, a direct port, and a coupled port;
a first diode having an anode connected to the direct port and a cathode connected to the ground;
a first matching circuit and a second diode connected in series between the direct port and the ground, the second diode having a cathode connected to the ground;
a third diode having an anode connected to the coupled port and a cathode connected to the ground;
a second matching circuit and a fourth diode connected in series between the coupled port and the ground, the fourth diode having a cathode connected to the ground; and
a controllable biasing-voltage supply connected to the direct port and the coupled port, thereby supplying the direct and coupled ports with a controllable biasing voltage.
In operation, the predistorter produces a controllable predistortion of the RF signal related to the controllable biasing voltage to cancel a distortion subsequently produced by the amplifier.
Still in accordance with the present invention, there is provided a predistorter for predistorting a RF signal subsequently injected in an amplifier, comprising:
a hybrid coupler comprising a RF input constituting an input of the predistorter supplied with the RF signal, a RF output constituting an output of the predistorter for supplying a predistorted version of the RF signal, a direct port, and a coupled port;
a first transistor connected between the direct port and the ground;
a second transistor connected between the coupled port and the ground; and
a controllable biasing-voltage supply connected to the first transistor and the second transistor, thereby supplying the first and second transistors with a controllable biasing voltage.
In operation, the predistorter produces a controllable predistortion of the RF signal related to the controllable biasing voltage to cancel a distortion subsequently produced by the amplifier.
According to the present invention, there is further provided a predistorting linearizer channel amplifier for processing an input signal subsequently supplied to a power amplifier, comprising:
a controllable input variable-attenuator and drive-amplifier circuit supplied with the input signal to attenuate and amplify the input signal;
a predistorter comprising a controllable phase-shifting and amplitude-adjusting path supplied with the attenuated and amplified input signal to distort the attenuated and amplified input signal and produce a predistorted output signal;
a controllable output variable-attenuator and drive-amplifier circuit supplied with the predistorted output signal to attenuate and amplify the predistorted output signal before supplying the predistorted output signal to the power amplifier;
a phase-shifting and amplitude-adjusting controller connected to the controllable input variable-attenuator and drive-amplifier circuit, the controllable phase-shifting a n d amplitude-adjusting path, and the controllable output variable-attenuator and drive-amplifier circuit; and
a bypass extending in parallel with the series circuit including the serially interconnected input variable-attenuator and drive-amplifier circuit, controllable phase-shifting and amplitude-adjusting path, and output variable-attenuator and drive-amplifier circuit, the bypass defining a bypass circuit established in response to a fault condition in the series circuit to bypass the faulty series circuit.
The foregoing and other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only with reference to the accompanying drawings.